Dissociative Carbamate Exchange Anneals 3D Printed Acrylates

Abstract

Relative to other additive manufacturing modalities, vat photopolymerization (VP) offers designers superior surface finish, feature resolution, and throughput. However, poor interlayer network formation can limit a VP-printed part's tensile strength along the build axis. We demonstrate that the incorporation of carbamate bonds capable of undergoing dissociative exchange reactions provides improved interlayer network formation in VPprinted urethane acrylate polymers. In the presence of dibutyltin dilaurate catalyst, the exchange of these carbamate bonds enables rapid stress relaxation with an activation energy of 133 kJ/mol, consistent with a dissociative bond exchange process. Annealed XY tensile samples containing a catalyst demonstrate a 25% decrease in Young's modulus, attributed to statistical changes in network topology, while samples without a catalyst show no observable effect. Annealed ZX tensile samples printed with layers perpendicular to tensile load demonstrate an increase in elongation at break, indicative of self-healing. The strain at break for samples containing a catalyst increases from 33.9 to 56.0% after annealing but decreases from 48.1 to 32.1% after annealing in samples without a catalyst. This thermally activated bond exchange process improves the performance of VP-printed materials via self-healing across layers and provides a means to change Young's modulus after printing. Thus, the incorporation of carbamate bonds and appropriate catalysts in the VP-printing process provides a robust platform for enhancing material properties and performance.

Closed-Loop Additive Manufacturing: Dynamic Covalent Networks in Vat Photopolymerization

“…Smaldone and co-workers highlighted the potential of Diels–Alder chemistry in photocurable acrylate resins for VP. , A thermally reversible Diels–Alder cross-linker was incorporated in a polyacrylate network printed by SLA. Following a dissociative mechanism, materials based on Diels–Alder adducts have difficulties to retain their shape at elevated temperatures due to the retro-Diels–Alder reaction, which leads to deformations and a rough surface finish.…”

Intrinsic toughened conductive thermosetting epoxy resins: utilizing dynamic bond and electrical conductivity to access electric and thermal dual-driven shape memory

“…45 Reversible exchange reaction between carbamate bonds in the polyurethane system could be conducted at high temperature, which may endow these devised EPUs with dynamic performance. [46][47][48] In order to investigate the dynamic nature of the EPUs, a relatively regular curve was obtained by using DMA to analyze the stress relaxation characterization of EPU1 at different temperatures. As shown in Fig.…”

Vat Photopolymerization Additive Manufacturing of Tough, Fully Recyclable Thermosets

“…The chemical details, exchange mechanism, and stoichiometry of a particular DCB system can be tuned to access diverse behaviors ranging from full network relaxation for remolding, , interfacial reactions for self-healing, and backbone scission to revert to oligomers. , Even though several DCB systems have been incorporated in bulk photopolymers, they have been sparsely employed in DLP-based 3D printing to date. However, existing examples demonstrate the powerful ability of dynamic covalent chemistry to be used as a tool to modulate materials in time and space, including enhanced interlayer adhesion, postprinting modification, − and life cycle control. − …”

“…35,36 Even though several DCB systems have been incorporated in bulk photopolymers, they have been sparsely employed in DLP-based 3D printing to date. However, existing examples demonstrate the powerful ability of dynamic covalent chemistry to be used as a tool to modulate materials in time and space, including enhanced interlayer adhesion, 37 postprinting modification, 38−40 and life cycle control. 41−44 To further extend DCB use in light-based additive manufacturing, resin systems that are compatible with photopolymerization and readily incorporate dynamic monomers are needed.…”